Term risk Definition: The possibility of gain or loss. Risk the calculated probability of different events happening, is usually contrasted with uncertainty the possibility that any number of things could happen. For example, uncertainty is the possibility that you could win or lose $100 on the flip of a coin. You don't know which will happen, it could go either way. Risk, in contrast, is the 50 percent chance of winning $100 and the 50 percent chance of losing $100 on the flip of the coin. You know (or think you know) that your probability of winning or losing is 50 percent because the coin has a 50 percent chance of coming up either heads or tails.